The treatment of polyester to impart to it stain-release properties is well known in the art. The most common polyester used as fibers is polyethylene terephthalate which possesses a hydrophobic character, making its laundering (particularly as regards oily soil and oily stains) difficult. This is due in large part to the inherent low wettability of the polyester fibers. Oily soil or stain is difficult to remove in an aqueous laundering process since the oily material tends to become attached to the hydrophobic, or oleophilic, fibers. U.S. Pat. No. 3,959,230 describes a number of approaches used in the prior art to increase the hydrophilic character of polyester-containing fibers. Many of these approaches involve treating the surfaces of shaped polyester articles with copolymers of terephthalic acid and polyethylene glycol. The purpose of this treatment is to provide the polyester with a hydrophilic finish to reduce the tendency of the polyester to retain oily stains. U.S. Pat. No. 3,959,230 states that prior art approaches have generally been unsuccessful in soil-release performance due to lack of durability and marginal-to-unsatisfactory soil-release performance. These polymers apparently lack the necessary performance to polyester fibers under common laundering conditions, and the patentee teaches a polyester soil-release agent having durability to polyester comprising repeating units of ethylene terephthalate and polyethylene oxide terephthalate at a molar ratio of ethylene terephthalate units to polyethylene oxide terephthalate units of from about 25:75 to about 35:65, said polyethylene oxide terephthalate containing polyethylene oxide having a molecular weight of from about 300 to 700, the molecular weight of said soil-release polymer being in the range of from about 25,000 to about 55,000 and the melting point of said polymer being below 100.degree. C.
British Pat. No. 1,088,984 and its U.S. counterparts, U.S. Pat. Nos. 3,416,952 and 3,619,269 disclose the surface-modifying treatment of shaped articles made from essentially linear crystalline polyester with agents which co-crystallize with the crystalline polyester segments of the fibers. The agent of this patent is a water-insoluble crystallizable polymeric compound being characterized in that:
(A) it has a crystalline melting point above 100.degree. C., measured by the temperature of disappearance of birefringence, PA1 (B) it contains crystallisable segments of repeat units identical with the repeat units forming the crystallisable portions of the shaped polyester article, and PA1 (C) it contains at least one active group linked to the crystallisable segments in (B) by groups containing ester or amide linkages, said active groups serving to modify the surface of the shaped article, said active group being selected from at least one of the following: water-solvatable polymeric polyoxylalkylene groups as hereinafter defined, acetic groups comprising sulphonic acid, phosphonic acid, carboxylic acid or ionisable salts thereof, nitrogenous basic groups or ionisable salts thereof, antioxidant groups, groups which contain silicon- or fluorine-based water-repellent groups, polymeric groups containing a plurality of alcoholic hydroxyl radicals and polymeric groups containing a plurality of --CO--NH-- radicals. PA1 (1) 100 mole percent of dicarboxylic acids consisting essentially of PA1 (2) 100 mole percent of glycols consisting essentially of aliphatic glycols containing 2 to 10 carbon atoms and up to 4 non-peroxidic catenary oxygen atoms, of which glycols at least 30 mole percent is ethylene glycol. PA1 Water-Dispellability: Approximately 1 gram of polyester resin is put in a 125 ml jar and 99 ml of 20.degree. C. tap water is added. A cap is placed on the jar, which is then mounted on a reciprocating shaker for 2 hours. If no pieces of resin remain, the resin is termed water-dispellable. If some pieces of the resin remain, the mixture is transferred to a 250 ml beaker and heated to about 180.degree. F. (80.degree. C.) for 20 minutes. If no pieces of resin then remain, the resin is deemed water-dispellable. If, however, pieces of the resin can still be discerned, the resin is considered not to be water-dispellable.
British Pat. No. 1,088,984 discloses the addition of sulfonic acid and other ionic groups to impart dyeability to the polymers. The patentee does not require their use for stain-releasability.
Although British Pat. No. 1,088,984 discloses surface-modifying shaped polyester articles so as to render them antistatic and soil-releasing throughout many cleaning processes by treatment with a high concentration of a crystalline polyester polymer, and although other agents are described in the prior art for rendering polyester articles stain-releasant, it appears novel in the art to provide shaped polyester articles with a durable stain-releasing finish by treating the article with a water-dispellable non-crystalline polyester polymer.